If the book is by Claire Davies, buy it. You can check for yourself if you have trigger points around your shoulder, and then you can address them using manual therapy or the right stretches.

In any chronic joint pain situation, trigger points often come to play a role, even if the original cause was something else entirely. I have chronic problems with many joints, and my mother went through a phase where she bought me every book and device she heard of, including, God help me, a bra with magnets in it! I have thrown away or lost every product except my two books on trigger points, which I refer to all the time. They've made such a difference in how I feel.

Beware of one thing: There is a group of new-agey energy healers who go around scamming people under the title of "trigger point therapy." Their work has no value and they should not be supported or enriched in any way.